Quantification of tissue (e.g., skin) blood perfusion assessment continues to be of fast-growing interest amongst clinicians, with applications across many surgical and non-surgical specialties. Although simple binary assessment (flow versus no-flow) may be adequate for some clinic al applications, frequently, quantification relative to some standard is needed for many other clinical applications. Increasingly, quantification in absolute terms (e.g., volume/time as a measurement of flow) is of interest. However, quantitative assessment of absolute blood perfusion in tissue as a tool of clinical assessment has been elusive.
Photoplethysmography (PPG) is an optical technique used to detect blood volume changes in the microvasculature. The observed waveform in PPG correlates with heartbeat, and PPG-based technology has been deployed in commercially available medical devices for measuring parameters such as oxygen saturation, blood pressure and cardiac output.
Despite the relatively wide deployment of medical devices based on PPG detection, PPG has not been exploited to facilitate routine determination of absolute measurement of tissue blood perfusion. A methodology with such capabilities would be of significant value to clinicians, since it would make possible routine acquisition of tissue blood perfusion measurements having the dimensions of volume/time/area. Only measurements having such dimensions allow for valid, direct inter-site and inter-subject comparisons. Therefore, there is a need for methods and systems for quantitative assessment of absolute blood perfusion in tissue.